Multi-wavelength cross-connect optical switch

ABSTRACT

A cross-connect switch for fiber-optic communication networks employing a wavelength dispersive element, such as a grating, and a stack of regular (non-wavelength selective) cross bar switches using two-dimensional arrays of micromachined, electrically actuated, individually-tiltable, controlled deflection micromirrors for providing multiport switching capability for a plurality of wavelengths. Using a one-dimensional micromirror array, a fiber-optic based MEMS switched spectrometer that does not require mechanical motion of bulk components or large diode arrays can be constructed with readout capability for WDM network diagnosis or for general purpose spectroscopic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisionalapplication Ser. No. 60/038,172 filed on Feb. 13, 1997.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005] This invention relates to a cross-connect switch for fiber-opticcommunication networks including wavelength division multiplexed (WDM)networks, and more particularly to such an optical switch using a matrixof individually tiltable micro-mirrors.

[0006] 2. Description of the Background Art

[0007] Multi-port, multi-wavelength cross-connect optical switches withcharacteristics of large cross-talk rejection and flat passband responsehave been desired for use in wavelength-division multiplexed (WDM)networks. Four-port multi-wavelength cross-bar switches based on theacousto-optic tunable filter have been described (“IntegratedAcoustically-tuned Optical Filters for Filtering and SwitchingApplications,” D. A. Smith, et al., IEEE Ultrasonics SymposiumProceedings, IEEE, New York, 1991, pp. 547-558), but they presentlysuffer from certain fundamental limitations including poor cross-talkrejection and an inability to be easily scaled to a larger number ofports. Attempts are being made to address to this problem by dilatingthe switch fabric, both in wavelength and in switch number, to provideimproved cross-talk rejection and to expand the number of switched portsso as to provide an add-drop capability to the 2×2 switch fabric. Thisstrategy, however, adds to switch complexity and cost. Recently, Pateland Silberberg disclosed a device employing compactly packaged,free-space optical paths that admit multiple WDM channels spatiallydifferentiated by gratings and lenses (“Liquid Crystal and Grating-BasedMultiple-Wavelength Cross-Connect Switch,” IEEE Photonics TechnologyLetters, Vol. 7, pp. 514-516, 1995). This device, however, is limited tofour (2×2) ports since it relies on the two-state nature of polarizedlight.

BRIEF SUMMARY OF THE INVENTION

[0008] It is therefore an object of this invention to provide animproved multi-wavelength cross-connect optical switch which is scalablein port number beyond 2×2.

[0009] Another object of the invention to provide such an optical switchwhich can be produced by known technology.

[0010] Another object of this invention to provide such an opticalswitch with high performance characteristics such as basic low loss,high cross-talk rejection and flat passband characteristics.

[0011] Another object of the invention is to provide a fiber-opticswitch using two arrays of actuated mirrors to switch or rearrangesignals from N input fibers onto N output fibers, where the number offibers, N, can be two, or substantially larger than 2.

[0012] Another object of the invention is to provide a fiber-opticswitch using 1-D arrays of actuated mirrors.

[0013] Another object of the invention is to provide a fiber-opticswitch using 2-D arrays of actuated mirrors.

[0014] Another object of the invention is to provide a fiber-opticswitch using mirror arrays (1-D or 2-D) fabricated using micromachiningtechnology.

[0015] Another object of the invention is to provide a fiber-opticswitch using mirror arrays (1-D or 2-D) fabricated using polysiliconsurface micromachining technology.

[0016] Another object of the invention is to provide a fiber-opticswitch using arrays (1-D or 2-D) of micromirrors suspended by torsionbars and fabricated using polysilicon surface micromachining technology.

[0017] Another object of the invention is to provide a fiber-opticswitch with no lens or other beam forming or imaging optical device orsystem between the mirror arrays.

[0018] Another object of the invention is to provide a fiber-opticswitch using macroscopic optical elements to image or position theoptical beams from the input fibers onto the mirror arrays, and likewiseusing macroscopic optical elements to image or position the opticalbeams from the mirror arrays onto the output fibers.

[0019] Another object of the invention is to provide a fiber-opticswitch using microoptics to image or position the optical beams from theinput fibers onto the mirror arrays, and likewise using microoptics toimage or position the optical beams from the mirror arrays onto theoutput fibers.

[0020] Another object of the invention is to provide a fiber-opticswitch using a combination of macrooptics and microoptics to image orposition the optical beams from the input fibers onto the mirror arrays,and likewise using combination of macrooptics and microoptics to imageor position the optical beams from the mirror arrays onto the outputfibers.

[0021] Another object of invention is to provide a fiber-optic switch inwhich the components (fibers, gratings, lenses and mirror arrays) arecombined or integrated to a working switch using Silicon-Optical-Benchtechnology.

[0022] Another object of the invention is to provide a fiber-opticswitch using 2-D arrays of actuated mirrors and dispersive elements toswitch or rearrange signals from N input fibers onto N output fibers insuch a fashion that the separate wavelength channels on each input fiberare switched independently.

[0023] Another object of the invention is to provide a fiber-opticswitch as described above, using diffraction gratings as wavelengthdispersive elements.

[0024] Another object of the invention is to provide a fiber-opticswitch as described above, using micromachined diffraction gratings aswavelength dispersive elements.

[0025] Another object of the invention is to provide a fiber-opticswitch using fiber Bragg gratings as wavelength dispersive elements.

[0026] Another object of the invention is to provide a fiber-opticswitch using prisms as wavelength dispersive elements.

[0027] Another object of the invention is to provide a fiber-optic basedMEMS switched spectrometer that does not require mechanical motion ofbulk components nor large diode arrays, with readout capability for WDMnetwork diagnosis.

[0028] Another object of the invention is to provide a fiber-optic basedMEMS switched spectrometer that does not require mechanical motion ofbulk components nor large diode arrays, with readout capability forgeneral purpose spectroscopic applications.

[0029] Further objects and advantages of the invention will be broughtout in the following portions of the specification, wherein the detaileddescription is for the purpose of fully disclosing preferred embodimentsof the invention without placing limitations thereon.

[0030] An optical switch embodying this invention, with which the aboveand other objects can be accomplished, may be characterized ascomprising a wavelength dispersive element, such as a grating, and astack of regular (non-wavelength selective) cross bar switches using apair of two-dimensional arrays of micromachined, electrically actuated,controlled deflection micro-mirrors for providing multiport switchingcapability for a plurality of wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

[0032]FIG. 1 is a schematic diagram of an optical switch in accordancewith the present invention.

[0033]FIG. 2 is a schematic plan view of a single layer of the switchingmatrix portion of the optical switch shown in FIG. 1.

[0034]FIG. 3 is a diagrammatic plan view of a row of individuallytiltable micro-mirrors employed in the switch array portion of theoptical switch shown in FIG. 1.

[0035]FIG. 4 is a schematic diagram showing switching matrix geometry inaccordance with the present invention.

[0036]FIG. 5 is a schematic sectional view of a grating made in siliconby anisotropic etching.

[0037]FIG. 6 is a schematic diagram of an alternative embodiment of theoptical switch shown in FIG. 1 employing a mirror in the symmetry plane.

[0038]FIG. 7 is a schematic plan view of a single layer of the switchingmatrix portion of the optical switch shown in FIG. 6.

[0039]FIG. 8 is a schematic diagram of a WDM spectrometer employing anoptical switch in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Referring more specifically to the drawings, for illustrativepurposes the present invention is embodied in the apparatus generallyshown in FIG. 1 through FIG. 8, where like reference numerals denotelike parts. It will be appreciated that the apparatus may vary as toconfiguration and as to details of the parts without departing from thebasic concepts as disclosed herein.

[0041] Referring first to FIG. 1, a multi-port (N×N ports),multi-wavelength (M wavelength) WDM cross-connect switch 10 embodyingthis invention is schematically shown where, in the example shown, N=3.In this switch 10, the wavelength channels 12 a, 12 b, 12 c of threeinput fibers 14 a, 14 b, 14 c are collimated and spatially dispersed bya first (or input) diffraction grating-lens system 16. The grating-lenssystem 16 separates the wavelength channels in a direction perpendicularto the plane of the paper, and the dispersed wavelength channels arethen focused onto a corresponding layer 18 a, 18 b, 18 c of a spatialmicromechanical switching matrix 20. The spatially reorganizedwavelength channels are finally collimated and recombined by a second(or output) diffraction grating-lens system 22 onto three output fibers24 a, 24 b, 24 c. The input and output lens systems are each composed ofa lenslet array 26 (32) and a pair of bulk lenses 28, 30 (34, 36) suchthat the spot size and the spot separation on the switching matrix 20can be individually controlled. Two quarter-wave plates 38, 40 areinserted symmetrically around the micromechanical switching matrix 20 tocompensate for the polarization sensitivity of the gratings 42, 44,respectively.

[0042] Referring now to FIG. 2, a schematic plan view of a single layer18 a of the switching matrix 20 of FIG. 1 is shown. As can be seen inFIG. 2, six micromirrors 46 a through 46 f are arranged in two arrays 48a, 48 b that can be individually controlled so as to optically “couple”any of the three input fibers 14 a, 14 b, 14 c to any of the threeoutput fibers 24 a, 24 b, 24 c. Referring also to FIG. 3, an example ofthe structural configuration of a row of individually tiltablemicromirrors on the switch array can be seen. As shown in FIG. 3, eachmirror 46 a, 46 b, 46 c is suspended by a pair of torsion bars orflexing beams 50 a, 50 b attached to posts 52 a, 52 b, respectively.Note that each mirror also includes a landing electrode 54 on which themirrors land when they are deflected all the way down to the substrate.

[0043] The advantages of this switching matrix arrangement include lowcross talk because cross coupling between channels must go through twomirrors, both of which are set up to reject cross talk, low polarizationsensitivity, and scalability to larger numbers of input fibers than two(which is the limit for polarization-based switches). The preferredfabrication technology for the micromirror arrays is surfacemicromachining as disclosed, for example, in Journal of Vacuum Scienceand Technology B, Vol. 6, pp. 1809-1813, 1988 because they can be madeby this method as small as the optical design will allow, they can bebatch-fabricated inexpensively, they can be integrated with on-chipmicromachinery from materials such as polysilicon and they can beminiaturized so as to reduce the cost of packaging.

[0044] Referring now to FIG. 4, there are several factors to considerfor designing the switching matrix 20. FIG. 4 shows an example of twomirror arrays 56 a, 56 b where each array comprises a plurality ofmirrors, Na through Nn. The basic parameters are the Gaussian beamradium (ω₀) at the center of the switch, the mirror size in thehorizontal direction (s), the distance between the mirror arrays (p),the incident angle on the mirror arrays (β), and the maximum deflectionof the micromirrors (t). The maximum angular deflection (α) of theoptical beams is dependent on the maximum deflection and the mirror size(in the horizontal direction), or tan α=4t/s (the optical deflectionbeing twice that of the mechanical deflection and the mirrors beingtethered at their center points). Conditions that must be satisfiedinclude: (i) the optical beams must be sufficiently separated on themirrors to keep cross-talk at reasonable levels; (ii) the sizes of thearrays must be small enough such that no shadowing occurs; and (iii) thepath length differences through the switch must not introducesignificant variations in insertion loss.

[0045] If a Gaussian-beam formalism is used, the cross coupling of twoparallel beams of radius ω₀ offset by d is given as exp{−(d/ω₀)2}. Ifthis should be less than 40 dB, for example, the ratio C=d/ω₀ must belarger than 3. This minimum ratio applies to both fiber-channel(horizontal) separation and wavelength channel (vertical) separation.Since the beam radii are larger at the mirrors due to diffraction thanat the focus, the above conclusion does not strictly apply, but it maybe required that the spacing of the beams must be at least three timeslarger than the optical beam radius also at the mirrors. Thisrequirement also reduces the losses due to aperture effects toinsignificant levels. The minimum mirror spacing (which is larger orequal to the mirror size) is then expressed as:

s=Cω/cos β=C(ω₀/cos β){1+(λp/2πω₀ ²)²}^(½)

[0046] where C is a factor greater than 3, ω is the beam size at themirrors, and λ is the wavelength of the light. This requirement,together with the restrictions on angular deflection, puts an upperlimit on the number of fiber channels (=N) in the switch. If the maximumdeflection angle is assumed small, the maximum number of channels is:

N=1+{4π cos β/C ² λ}t

[0047] The corresponding array separation and mirror spacing are:

p=2πω₀ ²/λ

[0048] and

s=2^(½) Cω ₀/cos β

[0049] If C=3, β=0.3 radian and λ=1.55 micron, N is given by N=1+0.86twhere t is in micron. The conclusion is that the simple geometry of FIG.4 can be used to design relatively large switches. Using known surfacemicromachining techniques, switches with three fiber channels can befabricated with a total sacrificial layer thickness of 2.75 micron.Larger switching matrices will require thicker sacrificial layers, suchas 8.1 micron for N=8 and 17.4 micron for N=16. These thicknesses can beobtained by simply using thicker sacrificial layers or by usingout-of-plane structures, or through a combination of these.

[0050] The minimum beam radium ω₀ is determined from the requirementthat the first mirror array should not obstruct the beams after they arereflected from the second mirror, and that the second mirror arrayshould not obstruct the beams before they reach the second mirror. If Nis maximized, C=3, β=0.3 radian and λ=1.55 micron, the beam radium inmicron must be larger than the number of fiber channels, or ω₀>N micron.The requirement of maximum path length difference is less restrictive(ω₀>0.8(N−1) micron). In general, the mirrors should be made as small aspossible because miniaturization of the mirrors leads to increasedresonance frequencies, lower voltage requirements and better stability.For N=3, ω₀ should preferably be on the order of 3 micron, leading to amirror spacing of s=13.3 micron. Mirrors of this size, as well asmirrors suitable for larger matrices are easily fabricated by a standardsurface micromachining process. This implies that micromachinedswitching matrices can be scaled to large numbers of fiber channels(e.g., N=16).

[0051] The minimum mirror separation in the wavelength-channel dimensionmay be smaller than the mirror separation s given above by the factor ofcos β because the mirrors are not tilted in that direction. The spacing,however, may be larger because there is no switching in the wavelengthdirection and there is no maximum angle requirement. It may be preferredto add 20 to 30 micron of space between the mirrors for mirror posts(see FIG. 3) and addressing lines. For a switch with N=3 and s=110micron, for example, a preferred separation in the wavelength dimensionmay be on the order of 130 micron. If the Littrow configuration is used,the required size of the Gaussian-beam radium on the grating is:

ω_(g) =C _(w)λ²/2πΔλ tan θ_(c)

[0052] where C_(w) is the ratio of beam separation to beam radium in thewavelength dimension, Δλ is the wavelength separation between channelsand θ_(c) is the incident angle (which equals the diffraction angle inthe Littrow configuration). With C_(w)=5.2 (25 micron beam radium and130 micron wavelength-channel separation), λ=1.55 micron, Δλ=1.6 nm(“the MONET standard”) and θ_(c)=45 degrees, ω_(g) is 1.2 mm (the orderof diffraction m being 1). This means that the long side of the gratingperpendicular to the grooves must be on the order of 5.3 mm and thefocal length f₂ of the second lens (the one between the grating and themicroswitches) should be about 60.8 mm.

[0053] The rotation of the grating about an axis perpendicular to theoptical axis and the grating grooves require a corresponding reductionof the grating period by Λ=mλ cos φ/(2 sin θ_(c)) where φ is therotation angle of the grating. If m=1, λ=1.55 micron, θ_(c)=45 degreesand φ=30 degrees, the grating period is 0.95 micron.

[0054] In a simple system without the microlens arrays shown in FIG. 1,the magnification of the input plane onto the switching matrix is givenby the ratio of the focal length f₂ of the second lens to the focallength f₁ of the first lens (e.g., lens 28 between the lenslets 26 andgrating 42). The role of the lenslet is to allow a differentmagnification for the mode size and for the mode spacing. In theoptimized geometry described above, the ratio of the mode separation tomode radius is 2^(½)C=4.24. If the fibers are as close together aspractically possible (e.g., 125 micron equal to the fiber diameter), theratio on the input is 125/5=25. The mode radius therefore must bemagnified 5.9 times more than the mode spacing. This can be accomplishedin several ways.

[0055] According to one method, lenslets are used to magnify the fibermodes without changing the mode separation. The lenslets are placed lessthan one focal length in front of the fibers to form an imaginarymagnified image of the fiber mode. Ideally, the lenslet diameters shouldbe comparable to or smaller than the fiber diameter, allowing theminimum fiber separation and a short focal length of the first lens tobe maintained. According to another method, the fiber mode is expandedadiabatically over the last part of its length by a heat treatment so asto out-diffuse the core. Mode size increase on the order of 4 times canbe accomplished.

[0056] According to still another method, the fibers are thinned down ormicroprisms are used to bring the modes closer together without changingthe mode size.

[0057] The first two methods require the same magnification or reductionof the input field. The third method has the advantage that lessreduction is needed, leading to smaller systems. If N=3, ω₀=25 micron,s=110 micron and f₂=60.8 mm, the required magnification is 0.84. Iflenslets of 125 micron diameter are used, the required focal length f₁of the first lens is 72.4 mm. If lenslets of 200 micron diameter areused, the required magnification is 0.525 and the required focal lengthf₁ of the first lens is 115.8 mm.

[0058] Parameters of a switch according to one embodiment of thisinvention with three input channels and three output channels aresummarized in Table 1.

[0059] Referring again to FIG. 3, the switching matrix design shown iscompatible with the MUMP (the Multiuser Micro Electro-Mechanical SystemProcess at the Microelectronics Center of North Carolina) and its designrules. The full switching matrix includes two arrays each with eightrows of the mirrors shown. The mirrors are actuated by an electrostaticfield applied between the mirror and an electrode underneath (notshown). Each of the mirrors in the switching matrix has three states,but the mirrors in the three rows do not operate identically. Thecentral mirror may send the beam to either side, while the outer mirrorsonly deflect to one side. According to one design, the two on the sidesare mirror images of each other, the center mirror being either in theflat state (no voltage applied) or brought down to the point where ittouches the substrate on either side. The electrode under the centralmirror is split in two to allow it to tilt either way. The side mirrorsalso have a state that is half way between the flat state and the fullypulled-down state. This may be achieved by having continuous controlover the mirror angles. Although this is complicated by theelectromechanical instability of parallel plate capacitors because, asthe voltage on the plates is increased, the capacitance goes up and thisleads to a spontaneous pulling down of the mirror when the voltage isincreased past a certain value, this effect can be avoided either bycontrolling the charge rather than the voltage on the capacitors, or byusing an electrode geometry that pushes the instability point past theangle to be accessed. Charge control utilizes the full range of motionof the mirrors but complicates the driver circuitry for the switch. Itmay be preferable to use electrode geometry to achieve the requirednumber of states.

[0060] When the MUMP process is used, the mirror size has a lower limitimposed by the minimum cross section that can be defined in thisprocess. To achieve large tilt angles without too much deflection of therotation axis of the mirror, the flexing beams must be kept short. Theshorter the flexing beam, the larger the mirrors must be for theelectrostatic force to be able to pull the mirrors down. Calculationsshow that the two side mirrors have the required angle when pulled downif use is made of beams that are 15 to 20 micron long, depending on theexact value of the material constants. For the voltage requirement to beacceptable, the mirror size must be on the order of 100×100 micron. Thebeams of the central mirror may be slightly longer, the maximum anglefor the central mirror being half that of the side mirrors. The geometryas shown in FIG. 3 ensures that the side mirrors can be tilted to halftheir maximum angles before reaching the electrostatic instability. Thecorresponding resonance frequencies are on the order of 20 to 50 Khz.FIG. 3 shows one of 8 layers of micromirrors in the switching matrixdescribed above; that is, the mirrors are separated by 110 micron in thehorizontal (fiber-channel) direction and by 130 micron in the vertical(wavelength-channel) direction. Two such arrays make up a switchingmatrix as shown in FIG. 2. The mirrors are shown on landing electrodes,that are shorted to the mirrors, when deflected all the way down to thesubstrate. Addressing lines and shorts are not shown in FIG. 3.

[0061] The whole switch may be fabricated in so-called silicon-opticalbench technology. The lenses, the switching arrays and the in/outmodules may be integrated, but commercially available dielectricgratings are too bulky for this technology. Microgratings may bedeveloped, based on anisotropic etching of silicon. Etching of the <100>surface of silicon through rectangular etch masks that are aligned withthe [111] directions of the substrate, creates V-shaped grooves definedby the <111 > crystallographic planes of silicon. An array of suchV-grooves 56 constitutes a grating that can be used in the Littrowconfiguration as shown in FIG. 5. The spacing between grooves can bemade arbitrarily small (e.g., 1 micron) by under-etching the mask andsubsequently removing this layer. The Littrow angle, which is determinedby the crystalline planes of silicon, is equal to 54.7 degrees. Bytaking advantage of the well-defined shape of a unit cell of thegrating, it is possible to obtain high diffraction efficiency in higherorder diffraction modes, the V-grooves constituting a blazed gratingoperated on higher orders. Higher-order operation means that thewavelength dependence of the diffraction efficiency increases. It can beshown that with 8 wavelengths separated by 1.6 nm centered at 1.55micron and the grating geometry of FIG. 5, the diffraction order can beincreased to m=15 with less than 1% variation in the diffractionefficiency between wavelength channels. With m=15, λ=1.55 micron,θ_(c)=54.7 degrees and φ=30 degrees, the grating period is calculated tobe Λ=12.3 micron. V-grooves with this spacing can be easily patternedand etched by using standard micromachining technology. V-groovegratings fabricated in this way can be metallized and used as gratingsdirectly, or be used as a mold for polysilicon microgratings that can berotated out of the plane by using micro-hinges. A potentially veryimportant additional advantage of higher-order gratings, as describedhere, is the reduced polarization sensitivity as compared to first-ordergratings. Since the periodicity is much larger than the wavelength, thediffraction will be close to being independent of polarization. Still,two wave plates may be used to compensate for residual polarizationsensitivity due to oblique angle reflections.

[0062] Referring now to FIG. 6 and FIG. 7, the fiber-optic switch, beingsymmetric about it's center, can be implemented with a symmetry mirror58 in the symmetry plane 60. This essentially cuts the component countin half. The output channels may either be on the input fibers andseparable by optical rotators (not shown) or on a separate output fiberarray (not shown) that is placed above the input array. In the lattercase, the micromirror array 62 and the symmetry mirror 58 are slightlytilted about an axis, such that the light is directed to the outputfiber array.

[0063] It will be appreciated that the fiber-optic switch of the presentinvention can serve network functions other than a traditional N×N×M(where M is the number of wavelengths in a WDM system).

[0064] It will further be appreciated that the fiber-optic switch of thepresent invention can be used in connection with diagnostic tools forWDM networks. WDM network management systems and software requireknowledge of the state of the entire network. Knowledge of the state ofthe many distributed optical channels is especially important. Themanager requires confirmation of whether or not a channel is active, itpower and how much a channel optical frequency has drifted as well asthe noise power level. Furthermore, this knowledge permits managementsoftware to identify, isolate, and potentially rectify or route aroundphysical layer faults.

[0065] Clearly network management requires numerous channelspectrometers that may be deployed in large number at affordable prices.Traditionally, such spectrometers are fabricated from gratings andlenses while an electronically scanned diode array or a mechanicallyscanned grating provide spectral information. Unfortunately, diode arraytechnology at 1.55 microns, and 1.3 microns, the preferredcommunications wavelengths, is immature. Such arrays are much morecostly and unreliable than those available for the visible spectralregion. Moving gratings are bulky and commercial system based on thisapproach are too costly for wide spread use in production networks.

[0066] Accordingly, a variation of the network switch described abovecan be employed to provide the desired functionality. Referring to FIG.8, an in-line WDM spectrometer 64 in accordance with the presentinvention is shown. In the embodiment shown in FIG. 8, WDM opticalsignals 66 emanating from an input fiber 68 would be collimated anddiffracted from the grating 70 forming a high resolution spatiallydispersed spectrum at the lens 72 focal plane. A single MEMS switcharray 74 would be placed at the lens focal plane, thus permitting thedeflection of individual optical channels or portions of a channel byone or more mirrors in the array. A quarter-wave plate 76 is insertedsymmetrically around the switching array 74 to compensate for thepolarization sensitivity of the gratings 70. A single infrared diodedetector 78 and focusing lens (not shown) would be placed in the returnpath of the reflected, and suitably displaced, return beam after asecond grating diffraction from grating 70. A full spectrum can thenobtained by scanning a deflection across the mirror array. Hence, asynchronized readout of the single photo diode yields the full spectrumto the management software.

[0067] The input fiber 68 and output fiber 80 can be arranged in avariety of ways. For example, they can be arranged side by side in theplane as shown in FIG. 8. An alternative would be to place the outputfiber over or under the input fiber. A further alternative would be touse the same fiber for the input and output paths, and separate thesignals using an optical circulator or the like.

[0068] The micromirror array 74 is preferably a one-dimensional arraywith one mirror per wavelength. Each mirror would thus operate in one oftwo states; the mirror either sends its corresponding wavelength to theoutput fiber 78 or is tilted (actuated) so that its correspondingwavelength is sent to the detector 76. In normal operation, only one ofthe mirrors is set up to deflect its wavelength to the detector.

[0069] Note also that, if the output fiber if removed and replaced by abeam sink (not shown), the spectrometer will still function althoughsuch an embodiment could not be used in an in-line application.

[0070] The invention has been described above by way of only a limitednumber of examples, but the invention is not intended to be limited bythese examples. Many modifications and variations, as well as designchanges to significantly reduce the overall size, are possible withinthe scope of this invention. For example, the beam radius in theswitching matrix may be reduced. The no-obstruction criterion allows achange to ω₀=5 micron for a 4-fiber switch, and this allows the focallength of both lenses to be reduced by a factor of 5. As anotherexample, the micromachining technology may be improved to place themirrors closer. The posts (as shown in FIG. 3) and addressing lines maybe moved under the mirrors to reduce the beam radium on the grating by afactor of 1.2. Together with the increased diffraction angle of amicromachine grating (say, to 54.7 degrees from 45 degrees), the focallengths of the lenses can be reduced by a factor of 1.7. As a thirdexample, the fiber modes may be brought closer together on the in/outmodules. If the mode spacing is reduced from 200 micron to 22.2 micron,the first and second lenses may have the same focal length (such thatmagnification=1). In addition, advanced designs may reduce the number ofrequired components. The switch may be designed so as to be foldableabout its symmetry point such that the same lenses and the same gratingwill be used both on the input and output sides. In summary, it is to beunderstood that all such modifications and variations that may beapparent to an ordinary person skilled in the art are intended to bewithin the scope of this invention.

[0071] Although the description above contains many specificities, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of the presently preferredembodiments of this invention. Thus the scope of this invention shouldbe determined by the appended claims and their legal equivalents. TABLE1 Components Parameter Values Input/output fibers Fiber channels: 3Standard single mode fiber Input-output MONET standard: wavelengthsCenter wavelength: 1.55 micron Wavelength channels: 8 Wavelengthseparation: 1.6 nm Lenslets Ball lens, 200-micron-diameter n < 1.6 Firstlens Bulk lens f₁ = 125.5 mm Grating Period: 0.95 micron Diffractionangle: 45 degrees Size: >6 mm Second Lens Bulk lens f₂ = 78.5 mmSwitching matrix N = 3 Mirror spacing: Fiber dimension: 110 micronWavelength dimension: 130 micron Array spacing: 2.5 mm Thickness ofsacrificial layer: 2.75 micron

What is claimed is:
 1. A fiber optic switch, comprising an array ofactuated mirrors for switching optic signals from a plurality of inputoptic fibers onto a plurality of output optic fibers.
 2. A fiber opticswitch as recited in claim 1 , wherein separate wavelength channels oneach input optic fiber are switched independently by said array ofmirrors.
 3. A fiber optic switch as recited in claim 1 , furthercomprising a plurality of optical elements for positioning optical beamsfrom said input optic fibers onto said array of mirrors.
 4. A fiberoptic switch as recited in claim 1 , further comprising a plurality ofoptical elements for positioning optical beams reflected from said arrayof mirrors onto said output fibers.
 5. A fiber optic switch as recitedin claim 1 , further comprising: (a) a wavelength dispersive element;and (b) a plurality of lenses associated with said first wavelengthdispersive element; (c) wherein said wavelength dispersive element andsaid plurality of lenses position optical beams from said input opticalfibers onto said array of mirrors.
 6. A fiber optic switch as recited inclaim 5 , wherein said wavelength dispersive element comprises adiffraction grating.
 7. A fiber optic switch as recited in claim 5 ,wherein said wavelength dispersive element comprises a prism.
 8. A fiberoptic switch as recited in claim 5 , further comprising: (a) a secondwavelength dispersive element; and (b) a second plurality of lensesassociated with said second wavelength dispersive element; (c) whereinsaid second wavelength dispersive element and said second plurality oflenses position optical beams reflected by said array of mirrors ontosaid output optic fibers.
 9. A fiber optic switch as recited in claim 8, wherein at least one of said wavelength dispersive elements comprisesa diffraction grating.
 10. A fiber optic switch as recited in claim 8 ,wherein at least one of said wavelength dispersive elements comprises aprism.
 11. A fiber optic switch, comprising: (a) an array of actuatedmirrors for switching optic signals from a plurality of input opticfibers onto a plurality of output optic fibers; (b) a wavelengthdispersive element; and (c) a plurality of lenses associated with saidwavelength dispersive element; (d) wherein said wavelength dispersiveelement and said plurality of lenses position optical beams from saidinput optical fibers onto said array of mirrors.
 12. A fiber opticswitch as recited in claim 12 , wherein separate wavelength channels oneach input optic fiber are switched independently by said array ofmirrors.
 13. A fiber optic switch as recited in claim 11 , wherein saidwavelength dispersive element comprises a diffraction grating.
 14. Afiber optic switch as recited in claim 11 , wherein said wavelengthdispersive element comprises a prism.
 15. A fiber optic switch asrecited in claim 11 , further comprising: (a) a second wavelengthdispersive element; and (b) a second plurality of lenses associated withsaid second wavelength dispersive element; (c) wherein said secondwavelength dispersive element and said second plurality of lensesposition optical beams reflected by said array of mirrors onto saidoutput optic fibers.
 16. A fiber optic switch as recited in claim 15 ,wherein at least one of said wavelength dispersive elements comprises adiffraction grating.
 17. A fiber optic switch as recited in claim 15 ,wherein at least one of said wavelength dispersive elements comprises aprism.
 18. A fiber optic switch, comprising: (a) an array of actuatedmirrors for switching optic signals from a plurality of input opticfibers onto a plurality of output optic fibers; (b) a first wavelengthdispersive element; (c) a first plurality of lenses associated with saidfirst wavelength dispersive element; (d) a second wavelength dispersiveelement; and (e) a second plurality of lenses associated with saidsecond wavelength dispersive element; (f) wherein said first wavelengthdispersive element and said first plurality of lenses position opticalbeams from said input optical fibers onto said array of mirrors andwherein said second wavelength dispersive element and said secondplurality of lenses position optical beams reflected by said array ofmirrors onto said output optic fibers.
 19. A fiber optic switch asrecited in claim 18 , wherein separate wavelength channels on each inputoptic fiber are switched independently by said array of mirrors.
 20. Afiber optic switch as recited in claim 18 , wherein at least one of saidwavelength dispersive elements comprises a diffraction grating.
 21. Afiber optic switch as recited in claim 18 , wherein at least one of saidwavelength dispersive elements comprises a prism.
 22. A fiber opticswitch, comprising: (a) a plurality of input optic fibers; (b) aplurality of output optic fibers: (c) an array of actuated mirrors forswitching optic signals from said input optic fibers onto said outputoptic fibers; (d) a first wavelength dispersive element; (e) a firstplurality of lenses associated with said first wavelength dispersiveelement; (f) a second wavelength dispersive element; and (g) a secondplurality of lenses associated with said second wavelength dispersiveelement; (h) wherein said first wavelength dispersive element and saidfirst plurality of lenses position optical beams from said input opticalfibers onto said array of mirrors and wherein said second wavelengthdispersive element and said second plurality of lenses position opticalbeams reflected by said array of mirrors onto said output optic fibers.23. A fiber optic switch as recited in claim 22 , wherein separatewavelength channels on each input optic fiber are switched independentlyby said array of mirrors.
 24. A fiber optic switch as recited in claim22 , wherein at least one of said wavelength dispersive elementscomprises a diffraction grating.
 25. A fiber optic switch as recited inclaim 22 , wherein at least one of said wavelength dispersive elementscomprises a prism.
 26. A fiber optic spectrometer, comprising: (a) afiber optic input path; (b) a fiber optic output path; (c) a detector;and (d) an array of actuated mirrors for switching optic signals fromsaid fiber optic input path to said fiber optic output path or saiddetector.
 27. A fiber optic spectrometer as recited in claim 26 ,further comprising: (a) a wavelength dispersive element; and (b) a lensassociated with said wavelength dispersive element; (c) wherein saidwavelength dispersive element and said lens positions optical beams fromsaid fiber optic input path onto said array of mirrors.
 28. A fiberoptic spectrometer as recited in claim 27 , wherein said fiber opticinput path and said fiber optic output path share a single optic fiber.29. A fiber optic spectrometer as recited in claim 27 , wherein saidfiber optic input path and said fiber optic output path are carried byseparate optic fibers.
 30. A fiber optic spectrometer, comprising: (a)an input optic fiber; (b) an output optic fiber; (c) a detector; (d) anarray of actuated mirrors for switching optic signals from said inputoptic fibers onto said output optic fiber or said detector; (e) awavelength dispersive element; and (f) a lens associated with saidwavelength dispersive element; (g) wherein said wavelength dispersiveelement and said lens positions optical beams from said input opticalfiber onto said array of mirrors.